Scalable manufacturing method of property-tailorable polyurea foam

ABSTRACT

The scope of this invention is to disclose the method of foaming a superior impact mitigation material, namely semi-closed cell hybrid polyurea foam, using scalable manufacturing process that is geometry-independent and allows for greater control of the resulting foam properties. while the process discussed herein, can be easily used to make complex geometries (e.g., padding foam for helmets, outsoles for walking and running shoes, body armors or other protection applications.

STATEMENT REGARDING FEDERALLY SPONSORED R&D

The U.S. Government may have certain rights in the invention pursuant toDepartment of Defense grant W911NF-14-1-0039.

CROSS-REFERENCE TO RELATED APPLICATIONS

Provided per USPTO rules by Application Data Sheet.

NAMES OF PARTIES TO JOINT RESEARCH AGREEMENT

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REFERENCE TO SEQUENCE LISTING

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STATEMENT RE PRIOR DISCLOSURES

Provided per USPTO rules by Application Data Sheet.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a process for making polyurea foam and productsmade using a foam made by the process.

Description of Related Art

Foams have been integrated in numerous impact mitigation mechanisms suchas protective pads, football helmets, walking and running shoes, andbiking helmets; to name a few. However, the functionalities ofpolymer-based foams are well understood for impact mitigation, theunderlying polymer's mechanical and physical properties as well as itsability to be foamed plays the bigger role in the effectiveness of thefoam. Basically, in order of polymer-based foam to be effective inmitigating impact, the foam layer must be able to reduce the amplitudeof the impact load while increasing the duration of the impact. In otherwords, the foam reduced the severity of the impact by reducing thetransmitted energy through energy absorbing mechanisms that includeelastic and plastic deformation of the foam materials.

Polyurea has been heavily investigated in the past decade and was foundto be very effective in mitigating impact in different applications(i.e., civilian and military) when used in a bulk form. Existing methodsare cumbersome, expensive, and not-scalable for processing to foampolyurea.

The ability to manufacture polyurea foam is inherently impeded due tothe viscosity of the polyurea mixture as well as the short pot life. Itis also hindered by the excellent adhesion properties of polyurea, whichmake the materials selection for the tooling and handling verychallenging. In previous attempts, vacuum oven was used to foam themixture but this process does not easily allow to control the thicknessand density of the foam. Additionally, the usage of vacuum oven limitsthe geometry of the foam. In other words, vacuum oven process can beused to make sheets with poor surface flatness with approximatethickness and density,

Therefore, there is a need for materials with inherent superior impactmitigation properties that can outperform others.

SUMMARY

The invention is a method of foaming a superior impact mitigationmaterial, namely polyurea, using scalable manufacturing process that isgeometry-independent and allows for greater control of the resultingfoam properties. The process discussed herein is used to make complexgeometries of foam products that can be used in various commercialproducts, e.g., padding foam for helmets, outsoles for walking andrunning shoes, body armors or other protection applications apparent tothose skilled in the field.

Accordingly, to address these and other issues in the prior art, thereis provided in a non-limiting preferred embodiment of the invention, aprocess of making a hybrid polyurea foam having a semi-closed cellmicrostructure, comprising the steps in a reaction having a ratio of 4:1by mass of an amine compound to an isocyanate compound, and having aratio of 8:3 by mass of the amine compound and the isocyanate compoundto deionized water: STEP 1. Mixing deionized water and an amine compoundin a mixing container at high speed; STEP 2. With the mixer turned off,adding the isocyanate compound to the mixing container, then mixing athigh speed the solution of isocyanate-water-amine to a foam; and, STEP3: Letting the solution sit after mixing, allowing time for theisocyanate-water-amine-reaction to occur, and then, after drainingexcess water from the mixing container, pour the mixture into a mold.

In a preferred embodiment, the isocyanate has the formula OCN—R1-NCO,where R1 is substituted or unsubstituted alkyl or aryl having 3-10carbons; and the polyamine has the formula H2N—R2-NH2 where R2 issubstituted or unsubstituted alkyl or aryl having 3-10 carbons.

In another preferred embodiment, the hybrid polyurea foam is configuredin a complex geometry or shape selected from the group consisting of:padding foam for helmets, outsoles for walking shoes, outsoles forrunning shoes, and padding foam for body armor.

In another preferred embodiment, the isocyanate is selected from thegroup consisting of an aromatic diisocyanate, toluene diisocyanate(TDI), methylenediphenyl diisocyanate (MDI), p-phenylene diisocyanate(PPDI), naphthalene diisocyanate (NDI), an aliphatic diisocyanate,hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate orhydrogenated MDI (HMDI), isophorone diisocyanate (IPDI), and mixturesthereof.

In another preferred embodiment, the amine is a Versalink amine.

In yet another non-limiting preferred embodiment of the invention, thereis provided a a process of making a hybrid polyurea foam having asemi-closed cell microstructure, comprising the steps in a reactionhaving a ratio of 4:1 by mass of an amine compound to an isocyanatecompound, and having a ratio of 8:3 by mass of the amine compound andthe isocyanate compound to deionized water: STEP 1: Removingcrystallization in a sample of an isocyanate compound by heating theisocyanate compound; STEP 2: Pre-Mixing a sample of deionized water anda sample of an amine compound in a mixing container; STEP 3: With themixer turned off and suspended above the mixing container, add theisocyanate to the mixing container, then mix the solution of deionizedwater-amine-isocyanate to a foam; and, STEP 4: Let the solution sitafter mixing, allowing time for the deionized water-amine-isocyanatereaction to occur, and then, after draining excess water from the mixingcontainer, pour the mixture into a mold.

There is also provided in a non-limiting preferred embodiment of theinvention, a process of making a hybrid polyurea foam having asemi-closed cell microstructure, comprising the steps: STEP 1: Removingcrystallization in a sample of methylene diphenyl diisocyanate (Isonate)by heating the Isonate to about 98 degrees Fahrenheit, holding at thattemperature for about 45 minutes, then immediately stirring vigorouslyfor 2 minutes, and allowing Isonate to return to room temperature; STEP2: Pre-Mixing a sample of deionized water and a sample ofpolytetramethyleneoxide-di-p-aminobenzoate (Versalink) in a mixingcontainer for about 45 seconds at about 10,000 rpm; STEP 3: With themixer turned off and suspended above the mixing container, add theIsonate to the mixing container, then mix the solution of deionizedwater-Versalink-Isonate for 45 seconds at roughly 10,000 RPM, moving themixer around the mixing container during mixing; and, STEP 4: Let thesolution sit for 45 seconds after mixing, allowing time for the reactionto occur, and then, after draining excess water from the mixingcontainer, pour the mixture into a mold.

In another preferred embodiment, there is provided a hybrid polyureafoam made according to the process of claim 1, wherein the hybridpolyurea foam comprises: (i) a plurality of large semi-closed cellshaving an average diameter of 370+/−162 μm, surrounded by (ii) aplurality of small semi-closed cells having an average diameter of69+/−162 μm.

In another preferred embodiment, there is provided a hybrid polyureafoam made according to the process of claim 1, wherein the hybridpolyurea foam comprises: (i) a plurality of large semi-closed cellshaving an average diameter of 200-500 μm, surrounded by (ii) a pluralityof small semi-closed cells having an average diameter of 30-90 μm.

In another preferred embodiment, there is provided wherein the hybridpolyurea foam is configured in a complex geometry or shape selected fromthe group consisting of: padding foam for helmets, outsoles for walkingshoes, outsoles for running shoes, and padding foam for body armor.

In another preferred embodiment, there is provided a method of preparinga polyurea component in a pre-treated non-stick mold, comprising thesteps in order: STEP 1: Measure out the necessary amounts of thefollowing ingredients: (a) Versalink P-1000(polytetramethyleneoxide-di-p-aminobenzoate); (b) Isonate 143L(methylene diphenyl diisocyanate)-(b)(i) The ratio of Versalink toIsonate must be 4:1 by mass; (c) Deionized Water-(c)(i) The ratio of thecombination of Versalink and Isonate to Deionized water must be 8:3 bymass; (d) To produce a foam sample with a thickness of 0.75 in, use thefollowing masses: Versalink: 429.9 g, Isonate: 107.5 g, Deionized Water:1,433.0 g; STEP 2: Heat Isonate to 98 degrees Fahrenheit. Hold at thistemperature for 45 minutes, then immediately stir vigorously for 2minutes. Allow Isonate to return to room temperature. (a) This is doneto break up any crystallization in the Isonate; STEP 3: Pre-Mixing(Deionized water and Versalink): (a) Add the deionized water and thenthe Versalink to a mixing container, (b) Use the SCILOGEX D500Homogenizer to mix the solution for 45 seconds at a Low setting, roughly10,000 RPM, moving the mixer around the mixing container during mixing;STEP 4: Mixing (Deionized water, Versalink, and Isonate): (a) With themixer turned off and suspended above the mixing container, add theisonate to the mixing container, (b) Use the SCILOGEX D500 Homogenizerto mix the solution for 45 seconds on a low setting, roughly 10,000 RPM,moving the mixer around the mixing container during mixing; STEP 5:Waiting period: (a) Let the solution sit for 45 seconds after mixing.This allows time for the reaction to occur; STEP 6: Immediately afterthe waiting period, drain excess water from the bottom of the mixingcontainer; STEP 7: Pour mixture into the mold, as evenly as possible;STEP 8: drain excess water by tilting the mold in multiple directions;STEP 9: place the mold lid into the mold, and attach bar clamps (1 perside, 4 total) to limit the expansion of the foam and inhibit the lidfrom rising or becoming uneven; and STEP 10: Leave sample in mold for 24hours, after 24 hours, remove the mold from the polyurea foam component.

In another preferred embodiment, there is provided a polyurea componentprepared according to the process claimed herein, wherein the polyureacomponent is configured in a complex geometry or shape selected from thegroup consisting of: padding foam for helmets, outsoles for walkingshoes, outsoles for running shoes, and padding foam for body armor.

In another preferred embodiment, there is provided a mold for preparingpolyurea foam component, comprising: a planar top cover attached byfasteners and stop-mechanism plates to a four-walled enclosure, thefour-walled enclosure having a bottom plate attached thereto byadditional fasteners, the planar top cover raised above a top surface ofthe four-walled enclosure by one or more spacers placed at the topsurface of each wall of the four-walled enclosure, one wall of thefour-walled enclosure having an aperture on a bottom surface configuredto allow pouring access into the four-walled enclosure, a metal meshcomponent is disposed within the aperture.

In another non-limiting preferred embodiment, the invention provides apolyurea foam having semi-closed cells, wherein the cell face has 3-10%holes, where it is 20% more efficient than standard prior polyureafoams, 44% better strength than standard prior polyurea foams, 15%better toughness than standard prior polyurea foams, 29% better specificmodulus of elasticity than standard prior polyurea foams, where the foamis mostly made of large cells 200-500 μm across surrounded by smallcells 30-90 μm across, wherein the foam is uniform in its mix of largecells surrounded by small cells and does not have a dense edge portionhaving stiff closed cell struts and small cell sheaths with a less denseinner portion, where the foam is functions in the elastic portion likeclosed cells and functions in the plateau region like open cell foams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical micrograph showing the entrapment of smallclosed-cells in the wall of large semi-closed cell and shows that theinventive polyurea foam is hierarchical because the large foam cells aresurrounded with smaller cells embedded in the walls around each cell.

FIG. 2 is scanning electron microscopy images showing highermagnification of the foam cell structure, and shows that the inventivepolyurea foam is hierarchical because the large foam cells aresurrounded with smaller cells embedded in the walls around each cell.

FIG. 3 is an illustration of an isometric view of the mold design.

FIG. 4 is a transparent illustration of the isometric view of the molddesign showing the fasteners.

FIG. 5 is an illustration and shows the exploded view of the mold designwith top cover having stop mechanisms, spacers, metal mesh, bottomplate, and fasteners.

FIG. 6 is an opening side view of one embodiment of the presentinvention.

FIG. 7 is an opening side view of one embodiment of the presentinvention with transparent views of fastener positions.

FIG. 8 is a top perspective view of a partial aspect of the presentinvention.

FIG. 9 is a top perspective view of a partial aspect of the presentinvention with transparent views of fastener positions.

FIG. 10 is a bottom view of one embodiment of the present invention withtransparent views of fastener positions.

FIG. 11 is a side view of one embodiment of the present invention.

FIG. 12 is a side view of one embodiment of the present invention withtransparent views of fastener positions.

FIG. 13 is a top view of one embodiment of the present invention.

FIG. 14 is a top view of one embodiment of the present invention withtransparent views of fastener positions.

FIG. 15 is a graph of Efficiency (y) vs. Stress (x) and shows comparisonbetween the efficiency of Polyurea foam (EML) and Market leading brand(D3O).

FIG. 16 is a graph of Stress (MPa) (y) vs. Stress (mm/mm) (x) and showscomparison between the efficiency of Polyurea foam (EML) and Marketleading brand (D3O).

FIG. 17(a)-(i) are a series of scanning electron microscopy imagesshowing higher magnification of the foam cell structure. FIGS. 7(a)-(i)show that the inventive polyurea foam is hierarchical because the largefoam cells are surrounded with smaller cells embedded in the wallsaround each cell.

FIG. 18 is a table comparing various features of the inventive polyureafoam (PU) versus a leading brand (LB).

FIG. 19 is a series (a-f) of SEM micrographs of (a-c) low relativedensity (EML227) and (d-f) high relative density (EML350) polyurea foamshowing cell perforation and deposits of microspheres.

FIG. 20 is an illustration of a Perforation formation process in (a)EML227 and (b) EML350 polyurea foams (insets capture the stretch marksdue to cell expansion during the foaming process).

FIG. 21 is an illustration of Self-reinforcement of foam byself-assembled polyurea microspheres on (a) EML227 and (b) EML350internal cell walls.

FIG. 22 is an illustration of Scanning Electron Microscopy scans of (a)EML227, (b) EML350 and (c)benchmark foam samples (arrows representdraining direction of diH2O).

FIG. 23 is an illustration of SEM micrographs of 0.21 relative densitypolyurea foam showing the hierarchical microstructure.

FIG. 24 is an illustration of Stress-strain data collected from polyureafoams with 0.21 (EML227) and 0.31 (EML350) relative density incomparison to a benchmark foam (

*=397 kg/m3).

FIG. 25 is an illustration of Comparison of the efficiency and G-levelbetween novel polyurea foam and closed-cell benchmark foam.

DETAILED DESCRIPTION OF THE INVENTION

This invention discloses two new innovations in manufacturing polyureafoam with high level of controlling the thickness and density that isscalable. First, manufacturing polyurea foam at room temperature andambient conditions, eliminating the need of vacuum oven. Second, castingpolyurea foams in sheets, where the mold can easily control thethickness while simultaneously controlling the density. As will bediscussed later, the geometry of the mold, thus the geometry of the foamproduct, is arbitrary since the mixture can be easily injected, pouredor casted in any geometry.

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventionto those skilled in the art. Like numbers refer to like elementsthroughout. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the full scope of theinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art. Nothing in this disclosure is to be construed as anadmission that the embodiments described in this disclosure are notentitled to antedate such disclosure by virtue of prior invention. Asused in this document, the term “comprising” means “including, but notlimited to.”

Many modifications and variations can be made without departing from itsspirit and scope, as will be apparent to those skilled in the art.Functionally equivalent methods and apparatuses within the scope of thedisclosure, in addition to those enumerated herein, will be apparent tothose skilled in the art from the foregoing descriptions. Suchmodifications and variations are intended to fall within the scope ofthe appended claims. The present disclosure is to be limited only by theterms of the appended claims, along with the full scope of equivalentsto which such claims are entitled. It is to be understood that thisdisclosure is not limited to particular methods, reagents, compounds,compositions or biological systems, which can, of course, vary. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art thatvirtually any disjunctive word and/or phrase presenting two or morealternative terms, whether in the description, claims, or drawings,should be understood to contemplate the possibilities of including oneof the terms, either of the terms, or both terms. For example, thephrase “A or B” will be understood to include the possibilities of “A”or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal subparts. As will be understood by oneskilled in the art, a range includes each individual member.

This research reports the synthesis of novel polyurea foam that bridgesthe gap between open and closed cell polymeric foams by self-foaming amixture of isocyanate, diamine, and deionized water in the absence ofheat and vacuum. The spherical, semi-closed cell structure was found tohave microscale large perforations on the surface of the cell due to theinteractions between adjacent expanding cell walls resulting from thegeneration of CO2 gas. Additionally, small holes were found to form andconcentrate along the bottom portion of the cells. The largeperforations and small holes contribute to the unique microstructure ofthe polyurea foam reported herein. The manufacturing process was alsofound to promote the nucleation and deposition of polyurea microsphereson the walls, adding a reinforcement phase while overcoming thefundamental interfacial issue between the matrix and reinforcement dueto both phases being made of the same material.

Referring now to FIGS. 1, 2, and 17 etc., it is shown that wesuccessfully and repeatedly manufactured hierarchical semi-closed cellpolyurea. Our polyurea foam is hierarchical because the large foam cellsare surrounded with smaller cells embedded in the walls around eachcell. We have also tested the flexibility of the manufacturing processdisclosed below to produce different thickness, different foam density,and different mechanical properties.

EXAMPLE Process of Manufacturing Foaming Polyurea

Polyurea is an elastomeric polymer that is made by mixing 4:1 ratio byweight of polytetramethyleneoxide-di-p-aminobenzoate (Air ProductsVersalink P-1000 Oligomeric Diamine) and polycarbodiimide-modifieddiphenylmethane diisocyanate (Dow Chemical Isonate 143L) to form ureabonds. The diamine extenders allow for the high flexibility as well asinitiate the reaction with the diisocyanate.

Changing the ratio of the diamine and diisocyanate influences themechanical and physical properties polyurea, hence it is the firstaspect in tailoring the properties of the foam to match the desiredapplication. Herein, we focused on 4:1 ratio since it represents themost common ratio for impact mitigating polyurea and it represent 1:21ratio by molecular weight. The blowing or foaming agent can be usedherein is tap, distilled or deionized water, where the form of water wasshown to have no effect of the foaming process. Herein, we useddeionized water for consistency and to impose a control on themanufacturing process for ease of comparison of fabricated polyurea foamproperties. The addition of water to the mixture of polyurea generatescarbon dioxide (CO2), which is the blowing gas responsible of formingthe foam cells. Changing the ratio of water foaming agent with respectto the ratio of polyurea mixture of diamine and diisocyanate affects theproduction of CO2 thus controlling the cell size and distribution,therefore it is the second aspect of tailoring the properties ofpolyurea foam. The biggest problem is thoroughly mixing the three foamconstituents (e.g., diamine, diisocyanate, and water) in largequantities, which is the reason we use a shear mixer to overcome thisproblem. Thus, our innovative process is highly scalable since the shearmixer specification can be scaled accordingly. First, the mold designand innovative features are discussed then we list the step-by-stepprocess to manufacture polyurea.

Example Mold Design

Referring now to FIGS. 3-14, there is provided a series of figures toillustrate one non-limiting embodiment of a design of the mold to createpolyurea foam sheet with adjustable thickness and density. The size ofthe mold can be easily adjusted to fabricate rectangular or square foamsheets with different specifications.

FIG. 3 shows the fully assembled mold in isometric view with fastenersshown and without the fasteners (FIG. 4). The fasteners can be replacedwith any other permanent or removable attachment mechanism such as glue,welding, or any other method apparent to those are skilled in the field.However, the mold shown in FIG. 3 has a square surface area, the changeof the surface area and geometry is easily accomplished by creating anew mold.

FIG. 5 shows the exploded view of the mold design, in which specificinnovations are highlighted. The top cover (item 1) of the mold is madeof polyethylene to ensure the flatness of the foam sheet and to preventadhesion between the mold and the foam materials during the curingprocess. The top cover thickness was chosen to compress the foam duringthe curing process due to its weight. Additional set of compressionclamps or weights can be used between the top cover and bottom plate toavoid top cover of floating above the mixture during curing withoutproper contact with the foam surface. The top cover has four metalbrackets (item 5) that act as a stop mechanism to prevent the top coverfrom displacing into the mold beyond the desired thickness. The secondinnovation to allow adjusting the thickness is the spacers (item 2),which are made from aluminum, but other materials can be used, withdifferent heights. When stacked together, the spacers control thethickness of the foam sheet by holding the top cover (item 1) atspecific distance from the bottom plate (item 4). A metal mesh (item 3)is placed on one side of the mold to block the foam slurry from escapingwhile allowing excess water to escape the mold.

Example Process of Mold Preparation

In one non-limiting preferred embodiment of the mold preparation aspectof the invention, there is provided a series of detailed steps.

STEP 1: Clean all surfaces of the mold that will contact the foam samplewith isopropanol

STEP 2: Create wax paper mold linings (two sheets needed. (a) Cut twosheets of Reynolds Wax Paper 15 inches long (standard width is 11.9 in).(b) Carefully apply strips of packing tape to cover the entire back sideof each sheet of wax paper. Packing tape strips must be at least 12 inlong and centered on the 15 in sheet. This must be done so there are nowrinkles or air bubbles present. Note: the wax paper surface must be theone to contact the foam, not the packing tape surface.

STEP 3: With the mold disassembled, apply a thin coat of silicone greaseto the bottom surface on the main aluminum body of the mold. Do not clogthreaded holes with grease.

STEP 4: Place one of the wax paper linings across this greased surfaceof the mold. (a) The tape surface will be facing upward from thisposition (wax paper surface should be pointing into the mold). Wax papershould be pulled tight with no wrinkles, and cover three sides of themold, excluding the side with the drain. Orient the wax paper lining sothat the long sides do not cover the side with the drain. (b) Secure thewax paper linings to the outside of the mold with packing tape on threesided (excluding the drain side). Create easy-to-remove pull tabs forthe tape, to simplify the removal process. (c) Carefully cut out circleswith a razor blade to expose the threaded holes covered by the wax paperlining (only 4 holes should have been covered if installed properly).(d) Reapply a thin coat of silicone grease to any areas that have beencovered by the lining, in the locations that received the original coatof silicone grease.

STEP 5: Attach the bottom plate of the mold to the main aluminum body ofthe mold. Fasten all joining bolts with a 5/16″ socket. Do not overtighten. Wipe off excess silicone grease.

STEP 6: Place the desired aluminum spacers on the top edges of the moldsides, placed in the center of each side (4 total). The spacers controlthe sample thickness. (a) Secure spacers with Scotch tape. Tape shouldbe used on the sides of the spacers only, so that the thickness is notaffected.

STEP 7: Use the second wax paper lining to cover the polyethylene moldlid. (a) Make sure the wax paper surface is facing into the mold andwill be the one contacting the foam (the packing tape surface should bein contact with the mold lid surface). (b) Attach the wax paper liningto the mold lid with packing tape on the two long sides of the lining.Create easy-to-remove pull tabs that extend all the way to the outside(the top) of the mold lid. This will allow the lining to be releasedwhile the mold is closed.

STEP 8: Spray all surfaces of the mold (lid and base pieces, includingthe wax paper linings) that will contact the foam sample, including theoutside of the drain, with Dry Film Release Agent and let dry. Spraywire mesh and magnets separately. Place all components on a spill tray,or other suitable surface when applying the spray.

STEP 9: Place the three magnets, in their indicated orientations, in thedrain slot outside of the mold. Place the wire mesh on the inside of themold in front of the drain. Manipulate the mesh to provide completecoverage of the drain.

Example Process of Preparing a Mixing Container

In one non-limiting preferred embodiment of the mixing containerpreparation aspect of the invention, there is provided a series ofdetailed steps.

STEP 10: Use a plastic disposable 5-quart bucket lining for mixing ofthe foam.

STEP 11: Create a splash-guard for the bucket using wax paper. (a)Attach the wax paper to the entire inside circumference (roughly 1 inchdown from the top surface) of the bucket with Scotch Tape. (b) Make aV-shaped cut roughly ¾ of the way down the wax paper splash-guard toallow the mixer to easily fit through, to ensure easy access during themixing process.

Example Shear Mixer Preparation

In one non-limiting preferred embodiment of the shear mixer preparationaspect of the invention, there is provided a series of detailed steps.

STEP 12: Disassemble all components of the shaft and mixing heads andplace them on a spill tray, or other suitable surface.

STEP 13: Generously spray the mixer components with Dry Film ReleaseAgent and let dry. Make sure to spray all threads and internal sectionsof the components.

STEP 14: Assemble the mixer and spray components lightly again with therelease agent and let dry.

Example Slab Molding Preparation

In one non-limiting preferred embodiment of the slab preparation aspectof the invention, there is provided a series of detailed steps.

STEP 15: Measure out the necessary amounts of the following ingredients:(a) Versalink P-1000 (polytetramethyleneoxide-di-p-aminobenzoate); (b)Isonate 143L (methylene diphenyl diisocyanate)—(b)(i) The ratio ofVersalink to Isonate must be 4:1 by mass; (c) Deionized Water—(c)(i) Theratio of the combination of Versalink and Isonate to Deionized watermust be 8:3 by mass; (d) To produce a foam sample with a thickness of0.75 in, use the following masses: Versalink: 429.9 g, Isonate: 107.5 g,Deionized Water: 1,433.0 g.

STEP 16: Heat Isonate to 98 degrees Fahrenheit. Hold at this temperaturefor 45 minutes, then immediately stir vigorously for 2 minutes. AllowIsonate to return to room temperature. (a) This is done to break up anycrystallization in the Isonate.

STEP 17: Place the assembled mold base on a laboratory scale: (a) Alignthe drain over a spill tray to contain the water spillage, (b) Elevatethe back edge of the mold opposite of the drain slightly (roughly ⅛ in),(c) Tare the scale, (d) Place blocks in the spill tray to set the moldonto. The position of the mold on the blocks must allow bar clamps to beattached on all 4 sides of the mold. The mold side opposite of the drainmust still be elevated ⅛ in when placed on the blocks, (e) Place a razorblade within reach. This will be used to make an incision in the bottomof the 5-quart bucket during the molding procedure.

STEP 18: Position the mold lid, bar clamps, and chemical ingredientswithin reach, to allow quick access during the molding process.

STEP 19: Pour cleaning agent (Citristrip Paint and Varnish StrippingGel) into a metal container to be used for cleaning the mixercomponents.

Slab Molding Procedure

STEP 20: NOTE: Requires 2 to 3 people (one to mix sample and immediatelybegin cleaning mixer, one to operate timer, pour sample into mold, closemold and attach bar clamps).

STEP 21: Pre-Mixing (Deionized water and Versalink): (a) Add thedeionized water and then the Versalink to the mixing container. Use atongue depressor with a flat edge to scrape all the substance into themixing container, (b) Use the SCILOGEX D500 Homogenizer to mix thesolution for 45 seconds. Use setting 1 on the mixer (Lowest setting,roughly 10,000 RPM). Submerge the mixer head roughly ⅔ of the way to thebottom of the container, at an angle of 15 degrees from the vertical.Slowly and consistently move the mixer around the mixing containerduring mixing.

STEP 22: Mixing (Deionized water, Versalink, and Isonate): (a) With themixer turned off and suspended above the mixing container, add theisonate to the mixing container. Use a tongue depressor with a flat edgeto scrape all the substance into the mixing container, (b) Use theSCILOGEX D500 Homogenizer to mix the solution for 45 seconds. Usesetting 1 on the mixer (Lowest setting, roughly 10,000 RPM). Submergethe mixer head roughly ⅔ of the way to the bottom of the container, atan angle of 15 degrees from the vertical. Slowly and consistently movethe mixer around the mixing container during mixing. The mixing shouldbegin immediately following the addition of the Isonate, as thisaddition with start the reaction.

STEP 23: Waiting period: (a) Let the solution sit for 45 seconds aftermixing. This allows time for the reaction to occur, (b) Remove thesplash-guard during this time, (c) Simultaneously, have the secondperson disassemble all components of the mixer head and shaftimmediately—(c)(i) Remove as much foam as possible from components(working time less than 10 minutes), (c)(ii) Once satisfied, place allcomponents in cleaning agent (Citristrip) and let sit for at least 15minutes.

STEP 24: Immediately after the waiting period, move mixing containerover the spill tray and make an incision (roughly 2 in long) on thebottom surface of the mixing container. (a) Allow all noticeable waterto drain out of the incision (notice the foam separation from thewater).

STEP 25: Pour mixture into the mold, as evenly as possible. (a) Do notscrape any of the mixture out of the mixing container. It is importantthat the mixture is added to the mold in a free-flowing pour to avoidunmixed portions that may accumulate on the sides and bottom of themixing container. (b) Measure the mass of the mixture poured into themold using the laboratory scale. Stop at the same number (or range)every time. (b)(i) For a 0.75 in sample thickness with thebeforementioned masses, this number is 527 g (a range of 520 to 527 isacceptable). (b)(ii) Record the exact mass in the mold.

STEP 26: Remove the mold from the scale and tilt toward the drain.Attempt to burst any water pockets and drain excess water by tilting themold in multiple directions. (a) Afterward, place the mold on the blocksin the spill tray.

STEP 27: Carefully place the mold lid into the mold. Make sure thealuminum tabs on the lid align with the aluminum spacers on the base ofthe mold. (The lid should be attached no Quickly attach bar clamps (1per side, 4 total) to limit the expansion of the foam and inhibit thelid from rising or becoming uneven.

STEP 28: Weigh the bucket with extra foam and record the value. Subtractbucket mass to obtain foam mass.

STEP 29: Leave sample in mold for 24 hours. Allow water to finishdraining into the spill tray and dispose of the water.

Example Foam Sample Removal

In one non-limiting preferred embodiment of the foam sample removalaspect of the invention, there is provided a series of detailed steps.

STEP 30: After 24 hours, remove the bottom plate of the mold from themain aluminum body of the mold, using a 5/16″ socket. (a) Carefullyremove the bottom plate without removing the wax paper lining from thesample.

STEP 31: Lift the easy-to-remove pull tabs on the mold lid and separatethem from the mold lid. (a) Carefully remove the mold lid withoutremoving the wax paper lining from the sample.

STEP 32: Carefully remove the foam sample from the aluminum surfaces ofthe mold by hand. Do not insert any sharp objects between the mold andthe foam sample. Slowly peeling the sample creates the cleanestseparation.

STEP 33: Once the foam sample is removed from the mold, slowly andcarefully remove the wax paper linings from both sides.

STEP 34: Optionally, weigh the foam sample and record the mass. (a)Measure the average thickness of the sample. Take two measurements (atleast) from each side of the sample, 8 total.

STEP 35: Optionally, weigh the bucket with the extra foam. (a) Recordthe number, subtract bucket mass to obtain foam mass.

Example Characterization of Efficiency

Referring now to FIG. 15 is a graph of Efficiency (y) vs. Stress (x) andshows comparison between the efficiency of the Polyurea foam of theinvention (EML) and Market leading brand (D3O).

FIG. 16 is a graph of Stress (MPa) (y) vs. Stress (mm/mm) (x) and showscomparison between the efficiency of the inventive Polyurea foam (EML)and Market leading brand (D3O).

FIG. 17(a)-(i) are a series of scanning electron microscopy imagesshowing higher magnification of the foam cell structure. FIGS. 7(a)-(i)show that the inventive polyurea foam is hierarchical because the largefoam cells are surrounded with smaller cells embedded in the wallsaround each cell.

Referring now to FIG. 18, Table 1 is a table comparing various featuresof the inventive polyurea foam (PU) versus a leading brand (LB). Wecompared the performance of our foam to the leading brand in impactmitigating foam, where our polyurea foam appears to be superior inmultiple aspects. Table 1 below shows that polyurea outperforms thecharacteristics of the leading brand foam per kilogram of the material.Specifically, polyurea foam was found to be 20% more efficient inmitigating impact than the leading brand.

The inventive Polyurea foam has 44%, 15%, and 29% better specificstrength, specific toughness, and specific modulus, respectively, thanthe leading brand currently in the market. It is worth noting that,using the method disclosed herein, it is easy to scale up tomanufacturing polyurea foam with comparable density, which willobviously outperform prior manufacturing methods.

Auxiliaries and additives (c) suitable for use in accordance with theinvention are, for example, the so-called internal release agents knownfrom the prior art. Preferred internal mold release agents are those ofthe type described, for example in DE-OS No. 19 53 637 (equals U.S. Pat.No. 3,726,952), DE-OS No. 21 21 670 (equals GB-PS No. 1,365,215), DE-OSNo. 24 31 968 (equals U.S. Pat. No. 4,098,731) and in DE-OS No. 24 04310 (equals U.S. Pat. No. 4,058,492). Preferred release agents includethe salts containing at least 25 aliphatic carbon atoms of fatty acidshaving at least 12 aliphatic carbon atoms and primary mono-, di- orpolyamines containing 2 or more carbon atoms or amide or ester aminescontaining at least one primary, secondary or tertiary amino group;saturated and/or unsaturated esters containing COOH— and/or OH-groups ofmono- and/or polybasic carboxylic acids and polyhydric alcohols havinghydroxyl or acid numbers of at least 5; ester-like reaction products ofricinoleic acid and long-chain fatty acids; polyricinoleic acids; saltsof carboxylic acids and tertiary amines; and also natural and/orsynthetic oils, fats or waxes.

The oleic acid or tall oil fatty acid salt of the amine containing amidegroups obtained by reacting N-dimethylaminopropylamine with oleic acidor tall oil fatty acid is particularly preferred.

In addition to these preferred release agents mentioned by way ofexample, it is also possible in principle to use other conventionalrelease agents known per se either individually or in admixture with thepreferred release agents mentioned previously. These other suitablerelease agents include the reaction products of fatty acid esters andpolyisocyanates according to DE-OS No. 23 19 648; the reaction productsof polysiloxanes containing reactive hydrogen atoms with mono- and/orpolyisocyanates according to DE-OS No. 23 56 692 (equals U.S. Pat. No.4,033,912); esters of polysiloxanes containing hydroxy methyl groupswith mono- and/or polycarboxylic acids according to DE-OS No. 23 63 452(equals U.S. Pat. No. 4,024,090); and salts of amino-polysiloxanes andfatty acids according to DE-OS No. 24 27 273 or DE-OS No. 24 31 968(U.S. Pat. No. 4,098,731).

The internal mold release agents mentioned above are used, if at all, ina total quantity of from about 0.1 to 25% by weight and preferably in atotal quantity of about 1 to 10% by weight, based on the reactionmixture as a whole.

Example Foam Sheets

Polyurea foam sheets (30.5 cm Long×30.5 cm Wide×1.9 cm Thick) werefabricated using a slab molding technique by combining Isonate® 143L(C15H10N2O2, modified Methylene Diphenyl Diisocyanate, DOW Industrial)and Versalink® P1000 (C70H124N2O16, oligomeric diamine, AirProductsInc.) with deionized water (diH2O) as the blowing agent. Two densityvariations of polyurea foam, 227.3±4.5 kg/m3 and 355.8±18.6 kg/m3, werefabricated by adjusting the amount of the diamine, cyanate, and diH2Owhile maintaining all other mixing and curing conditions constant. Afterpouring into the mold, samples were left to cure under ambientconditions in the absence of heat and vacuum. Samples extracted from thesheets were then coated with ˜6 nm of platinum and analyzed usingScanning Electron Microscopy (FEI, Quanta 450) in order to examine themicrostructure of the novel foam.

Example

FIG. 19 shows SEM micrographs of polyurea foams with low-relativedensity of 0.21 (EML227) and high-relative density (EML350) of 0.33.Image analysis of these micrographs reported that the average celldiameter of the EML227 foam was 134.5±108.5 μm, nearly 25% larger thanthose reported for EML350 (ϕc,350=90.9±48.9 μm). The variation betweenthe cell sizes is a function of the initial mixing ratio of thechemicals and the blowing agent as well as the final sheet thickness. Inshort, a slurry containing higher amounts of constituents was pouredinto the same mold volume, which resulted in crowding the entrapped gasbubbles and in turn yielded an overall smaller cell diameter. Finally,the spread in the distribution of the cell size is associated with ahierarchal structure, where the walls separating adjacent large cellstend to entrap cells with smaller diameters. Such hierarchalmicrostructure plays a major role in the mechanical behavior of the foamunder quasi-static.

The nucleation of CO2 gas bubbles due to the reaction between cyanateand diH2O continues to outwardly push on the surrounding walls resultingin the formation of the spherical microstructure shown in FIG. 19. Thetransformation of a spherical to polyhedral structure is impeded by theself-limiting chemical reaction creating CO2 and by the relatively shortcuring time of the polyurea elastomer. Nonetheless, the interplaybetween the internal gas pressure and the proximity of cells results inintersections between adjacent cells shown by the large perforationsaround the cell surface. The perforation formation process is clearlyillustrated in FIG. 20.

At the sites circled in red on FIG. 20, portions of the cell wallsappear to be much thinner sheaths, depicting areas where largeperforations would have been created if the cell wall expansion due toCO2 generation had continued. This mechanism is also confirmed byclosely examining the periphery of existing perforations, where theruptured edges are curled towards the cell with lower internal pressure.The rupture process occurs when the strength of the viscous polymersheath is well below that of the applied tension in the cell wall due tothe internal gas pressure. Additionally, the insets in FIG. 20 revealstretch marks on the cell walls formed by the gas pressure entrappedinside the cells during the curing process prior to setting, which isalso assisted by the pressure from the mold enclosure to control thedimensions of the sheets.

Example Semi-Closed Cell

Along with these large perforations, ubiquitous small holes arepreferentially located on one side of the cell, where the nucleation ofthe holes is correlated with the formation and precipitation of polyureamicrospheres. In essence, the formation of microspheres implies arelatively high local concentration of isocyanate that continuesreacting with the entrapped diH2O resulting in a localized CO2generation, hence the presence of the smaller holes. Overall, the cellfaces (or walls) of our novel polyurea foam contains only ˜7.6% and˜4.5% open-space, comprising of perforations and holes, for EML227 andEMT 350 respectively, hence its classification as ‘semi-closed cell’.Here, it is important to note that the newly reported ‘semi-closed cell’foam structure implies transversely-isotropic mechanical behavior whilepartially-open/partially-closed cell exhibits anisotropic behaviors onthe macroscale level.

FIG. 19b,e show the preferential direction at which the small holesnucleate on the lower portion of the foam cell. This phenomena isassociated with two concurrent processes. First, the aggressivemechanical mixing of amine and isocyanate into diH2O resulting in anemulsion of chemicals that in turn polymerizes and creates microspheres.Secondly, as the foam structure starts to form, its density is less thanthat of diH2O causing the foam slurry to rise and float above thesurface of the water. During the rising process, the water is drained(directions denoted with blue arrows on FIG. 19b,e ) at a relativelyhigh speed due to the size of the cell and in the process pulls thesuspended microspheres towards the bottom of the cell. Since thedeposition of the microspheres happens early in the curing stage, theongoing chemical reaction between un-polymerized cyanate and residualdiH2O on the bottom surface continue to locally produce CO2, hence thepresence of small holes at these locations.

One of the unique aspects of our novel polyurea foam is itsself-reinforcement by polyurea microspheres (FIG. 21). In other words,our foam is a self-assembled polymer/polymer composite, where themicrospheres improve the strength and increase the force required tobuckle the walls during loading scenarios such as impact forces. Themicrospheres are created through a modified precipitation polymerizationprocess, in which the isocyanate reacts with the amine moleculesemulsified in diH2O by the high speed, aggressive mechanical mixingprocess. In our process, the microspheres are a byproduct of the foamingprocess, where the initiator and suspension liquids are the same, beingdiH2O. The absence of elastic mismatch as well as chemical mismatchbetween the matrix phase (i.e., the cell walls) and reinforcement phase(i.e., microspheres) eliminates the inter-phasic region, hencesubstantially reducing the residual stresses at the interface betweenthe two composite phases.

Example Stress-Strain Characterization

Generally, foams are classified with either open-cell or closed-cellmicrostructure, where the mechanical, electrical, and thermal propertiesare defined as a function of the properties of the base material.Furthermore, the overall stress-strain behavior of polymeric foams canbe divided into three distinct stages corresponding to the elastic,plateau, and densification regions. Regardless of the region, scalinglaws can be used to extrapolate the properties of the foam from those ofthe base material as a function of the cell microstructure.

First in the elastic deformation region, scaling laws may be used tocalculate the elastic modulus of open-cell and closed-cell foams usingEquations 1 and 2, respectively.

$\begin{matrix}{\mspace{79mu} {\frac{E^{*}}{E_{s}} = {C_{1}\left( \frac{p^{*}}{p_{s}} \right)}^{2}}} & (1) \\{\mspace{79mu} {{\frac{E^{*}}{E_{s}} = {{C_{1}{\Phi^{2}\left( \frac{p^{*}}{p_{s}} \right)}^{2}} + {{C_{2}\left( {1 - \Phi} \right)}\frac{p^{*}}{p_{s}}} + \text{?}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (2)\end{matrix}$

Where, E* and Es are the elastic moduli of the foam and the basematerial, respectively;

* and

s are the densities of the foam and the base material, respectively; Φis the fraction of solid material contained in the cell edges; po is thefluid pressure inside the cell; ν* is the Poisson's ratio of the foam;and C1 and C2 are constants of proportionality determined from theexperimentally reported stress-strain curve. While the primarydeformation mechanism present in open-cell foams is from the bending ofthe cell edges (shown by the single term in Equation 1), the closed-cellfoams have three contributing mechanisms; namely cell edge bending, cellface stretching, and the compression of fluid inside the cell. Thesemechanisms are mathematically represented by the first, second and thirdterms in Equation 2, respectively. For typical engineered closed-cellfoams, Φ is bounded between zero and unity, where the latter will reduceEquation 2 to Equation 1 when the working fluid is air, or in the otherwords, the foam is then classified as open-cell. The second region ofthe stress-strain curve is characterized by a plateau behavior of thecompressive stress, where a minimal increase in compressive stress isassociated with a large increase in compressive strain. The plateauregion is attributed to the collapse of the cellular structure bybuckling in elastomeric foams or by plastic crushing (failure) in rigidfoams.

During an elastic matrix collapse, closed-cell foams have the addedcontribution of the pressure difference between the entrapped fluid andatmospheric pressure (pat). The onset of the plateau regime inelastomeric foams is defined by the elastic collapse strength (σ*),which can be el calculated using Equations 3 and 4 for open-cell andclosed-cell microstructures through a constant of proportionality (C3),respectively.

$\begin{matrix}{\mspace{79mu} {\text{?} = {{C_{s}\left( \frac{p^{*}}{p_{s}} \right)}^{2}\left( {1 + \sqrt{\left( \frac{p^{*}}{p_{s}} \right)}} \right)^{2}}}} & (3) \\{\mspace{79mu} {{\text{?} = {{{C_{3}\left( \frac{p^{*}}{p_{s}} \right)}^{2}\left( {1 + \sqrt{\left( \frac{p^{*}}{p_{s}} \right)}} \right)^{2}} + {\text{?}\text{?}}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (4)\end{matrix}$

For synthetic foams, the pressure inside dry cells is approximatelyequal to the atmospheric pressure when tested at low strain-rates,resulting in elimination of the second term in Equation 4.

The final stage of compression occurs when cell edges come into contactwith each other due to extreme collapse of the cellular matrix,resulting in densification. Additional strains induce compression of thematrix material itself, which marks the onset of the strain lockingphase causing a drastic spike in the stress; hence the slope of thestress-strain curve in this region approaches the Young's Modulus of thebase material. In other words, the onset of densification ischaracterized by the sharp non-linear rise in stress, where the criticalstrain (εc) at which the end of the plateau regime occurs can be definedby [5]

$\begin{matrix}{\mspace{79mu} {\text{?}{\text{?}\text{indicates text missing or illegible when filed}}}} & (5)\end{matrix}$

where, Cd is a constant of proportionality.

By considering the aforementioned scaling laws (Equations 1-4) thatrelate the properties of the base material to that of the foam, thereare two major fundamental findings pertaining to the behavior ofopen-cell versus closed-cell foams, specifically in the elastic andplateau regions. First, the underlying structure of open-cell foamcontains material only on the edges of the cell, which in turn reducesthe resistance to deformation of the cellular material. On the contrary,the closed-cell foam structure does not only have solid struts on theedges but also has polymer sheaths on the surface of the cell, which inturn increases the overall stiffness due to the additional contributionsof material and geometry, i.e. higher density indicates higher modulus(Equation 2).

In other words, the elastic modulus of open-cell foam is lower than thatof closed-cell foam, which delays the transition into the plateauregion.

The latter observation is deduced by carefully examining the equationsfor the elastic modulus implying Eopen<Eclosed and those for the onsetof the plateau showing σ*<σ*. Second, open-cell foams display linearplateau behavior el,open el,closed (relatively constant stress withincreasing strain) that is notably different than the increasing plateaubehavior (increasing stress with increasing strain) seen in closed-cellfoams. Additionally, when considering Equation 5 as the criteria for theend of the plateau region, the change in relative density can then beused to tune the strain percentage that marks the termination of thisregion, or in other words the start of the densification region. Thedesire to control the span of the plateau region stems from the abilityto control the amount of energy under the stress-strain curve withinthis region, hence improving the effectiveness of the foam to mitigatean incoming impact. For the same base material and cell geometry, therelative density of open-cell foam scales as (tl)2 while closed-cellfoam scales as (tl), thus a closed-cell foam structure exhibits a higherrelative density than that of an open-cell structure, due to theaddition of the cell wall material.

In short, closed-cell foams are a better performer in the elastic regionwhile open-cell foams are superior in the plateau region. Therefore, ahybrid foam structure that leverages the uniqueness of both cellularstructures is of scientific and industrial importance.

Example Sample Preparation

Polyurea foam sheets were prepared by casting a slurry into anadjustable-height mold. The slurry was first prepared by mixing Isonate®143L (modified Methylene Diphenyl Diisocyanate (MDI), DOW Industrial),Versalink® P1000 (oligomeric diamine, AirProduct Inc.) and distilledwater (diH2O) with specific ratios that are predetermined based on thedesired relative density of the foam. The mold was coated with nonstickTeflon spray to facilitate the quick release of the cured foam sheets.Once the constituents were mechanically and thoroughly mixed, theresulting slurry was quickly poured in the mold to avoid the initiationof curing within the mixing pot. The mold was covered with a nonstickhigh-density polyethylene block to control the thickness and maintainflatness of the top surface. However, although polyurea foam processesmay be known, the process delineated herein is distinguished as avacuum-free process.

This is important because of two specific aspects.

First, our polyurea foam slurry contains distilled water and thusplacing the foam to cure under vacuum accelerates the evaporation ofwater resulting in a poor control of the cell size and geometry.

Second, the addition of vacuum curing complicates the manufacturingprocess and may result in premature degradation of the cell materialbecause of the ongoing reaction between the cyanate and diH2O. Foamswith different mechanical properties were produced by carefullyadjusting the ratio of the foam constituents and the mechanical mixingduration. In all, two foam variations were fabricated with relativedensities of 0.21 and 0.33, referred to herein as EML227 and EML350,respectively.

Once the foam sheets were cured in ambient conditions in the mold for 24hours, the sheets were removed and left to air dry for 48 hours, atwhich it was noted that the foam sheets were water free. Samples with˜41 mm and ˜25 mm diameter were die cut (Mayhew Pro 66002) from the 0.21and 0.33 sheets using a hydraulic press (K. R. Wilson 37). Thethicknesses of the samples were found to be ˜17.2±0.4 mm and ˜15.9±0.5mm, respectively.

During the cutting process, it was noted that the speed of ram approachaffected the final geometry of the sample, thus a moderate ram approachspeed was used and resulted in uniform sample geometry, i.e., thehour-glass shape was drastically reduced.

Finally, in the effort to benchmark the newly synthesized polyurea foam,sheets of a closed-cell, proprietary formulation foam (referred tothereafter as benchmark) with a density of 397 kg/m3 were acquired fromoff-the-shelf products, cut with a nominal thickness of ˜14.4 mm andtested as discussed next.

Example Microstructure

FIG. 22 shows a comparison between the microstructure of the threetested foams. The perforations in the cells of EML foams are generallyclassified by their size in two major categories; namely small and largeperforations. While the latter is attributed to the intersection betweentwo adjacent cells and commonly observed in the upper portion of thecell, the former is a byproduct of the manufacturing process. Polyureamicrospheres are formed during the mixing process by precipitationpolymerization, where these microspheres are then attracted by gravityand suction forces during the draining of diH2O. By settling at thebottom, the microspheres nucleate new CO2 gas bubbles that create thesesmall perforations.

Finally, a close-up examination of the micrographs shown in FIG. 22revealed a hierarchical microstructure in the lighter polyurea foams,where large semi-closed cells with a size of 370±162 μm are surroundedby a relatively smaller cell sizes of 69±162 μm. This observation isclearly shown in the SEM micrographs presented in FIG. 23. In all, thehierarchical structure necessitates further investigation that is beyondthe scope discussed herein.

Example Experimental Protocol

All foam samples were tested using an Instron® 5843 Universal Load Frameinstrumented with a ±1 kN load cell at a strain-rate of approximately0.05 s-1. At the onset of each measurement run, samples were placedunder a preload pressure of 140 Pa to ensure proper contact. Aconditioning cycle was then performed twice at a cross-head speed of 250mm/min to 70% engineering strain, followed by a 6-minute (±1 min)recovery period. Thereafter, the samples were compressed at a cross-headspeed of 50 mm/min to 70% engineering strain. Following the experimentaltesting, the engineering stress-strain data for each of the three typesof foam materials was averaged and the deviation within each data setwas found to be below 3%. Thereafter, the average stress-strain data wasfurther analyzed to report the apparent modulus, the area under theelastic region, and the area under the entire stress-strain curve. Inaddition to the quasi-static analysis, predictions of the dynamicbehavior of the foams were performed following the methods.

Specifically, two dynamic properties are calculated from thestress-strain data to elucidate the performance of the foams underdynamic loading, namely the G-level and Efficiency. First, the maximumdeceleration, or maximum G-level, is defined as the ratio between theacceleration of the drop mass and the acceleration due to gravity, whichcan also be calculated using the energy per unit volume obtained fromthe integral of the stress-strain curve, expressed as

$\begin{matrix}{\mspace{79mu} {{G_{m} = \text{?}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (6)\end{matrix}$

Where σm and εm are the maximum stress and strain values produced by theimpact (respectively), H is the height from which the mass is dropped,and h is the thickness of the foam sample. Second, the efficiency of theenergy absorbed by the foam during a dynamic impact, which is definedherein based on the comparison of real and ideal foams. While thebehavior of real foam mimics those shown later in FIG. 3, an ideal foam,however, can be described as a foam that displays a constant stressvalue throughout the entirety of its compression history. Thus, theefficiency of energy absorption is the ratio of energy absorbed by areal foam compressed to the maximum strain produced by the loading eventto the energy absorbed by an ideal foam compressed throughout itsthickness as shown in Equation 7.

$\begin{matrix}{\mspace{79mu} {{E = \text{?}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (7)\end{matrix}$

The G-level and Efficiency as defined in Equations 6 and 7 are goodestimators of the performance of foam in response to dynamic loading,but the quasi-static derived data may overestimate the overall dynamicbehavior of foams.

Example Energy (Dissipated) Under Stress-Strain Curve

FIG. 24 shows the average compressive stress-strain behavior of EML227,EML350, and the benchmark foams when tested at a quasi-staticstrain-rate of approximately 0.05 s-1. The average was calculated basedon testing 25 samples of EML227, 3 samples of EML350, and 5 samples ofthe benchmark foam. While at low strain levels, the response of allthree foams is nearly identical.

However, each foam variation exhibits a significantly different responseat higher strains. The deviation in the responses starts around 15%strain, where the semi-closed cell structure of the EML foams gives riseto an interplay between the deformation due to the entrapment of gaswithin the cells and cell-face stretching associated with closed-cells,as well as cell-wall buckling, a hallmark of open-cell foams. In theabsolute sense, EMT 350 foam was found to outperform both EML227 andbenchmark foams. Interestingly, the energy under the stress-strain curveof EML227 (536 Pa/kg/m3) and benchmark foam (532 Pa/kg/m3) are withinthe experimental error of each other, thus elucidating the superiorityof EML 227 foam on per unit mass basis in attenuating impacts, since itis merely half the weight. On the other hand, when comparing EMT 350with the benchmark foam, the former was found to store (991 Pa/kg/m3),nearly double the energy under the stress-strain curve while being 12%lighter.

In the elastic region, the apparent modulus for EML227 was found to be0.64±0.11 MPa, while for EML350 it was found to be 0.88±0.16 MPa, andfor the closed-cell benchmark foam it was reported to be 0.69±0.03 MPa.Using Equations 1 and 2 to predict the elastic modulus of the newlysynthesized foams yielded an overestimation of ˜1.3 MPa for EML227 and˜1.7 MPa for EML350 by assuming either open-cell or closed-cellstructures, which corresponds to an error of roughly 100% when comparedwith the experimental results. Thus, neither EML227 nor EML350 can beclassified as purely open-cell or closed-cell foam.

FIG. 22 shows perforations in the microstructure that are ubiquitouslypresent in all the cells, hence eliminating the rationale for theclassification of separated partially-open/partially-closed cells.Therefore, the newly synthesized foams are classified as semi-closedcell, in which the cells are predominantly closed except for a fewregions at the bottom of the cells, where a high density of smallperforations are present as discussed earlier. In our effort toreconcile the difference between experimental data and theoreticalpredictions (using Equations 1 and 2) to better calculate the propertiesof our foam, the new foam structure was modeled as two elastic springsin series, where the top portion of the foam cell is represented by aclosed-cell spring (Equation 2) and the bottom highly-perforated sectionof the cell is modeled as an open-cell elastic spring (Equation 1).Hence, the effective modulus of semi-closed cell foams can be written as

$\begin{matrix}{\mspace{79mu} {{\text{?} = \frac{{C_{1}^{2}{\Phi^{2}\left( \frac{p^{*}}{p_{s}} \right)}^{2}} + {C_{1}{C_{2}\left( {1 - \Phi} \right)}\left( \frac{p^{*}}{p_{s}} \right)^{2}} + {C_{2}\frac{\text{?}\left( \frac{p^{*}}{p_{s}} \right)}{\text{?}\left( {1 - \frac{p^{*}}{p_{s}}} \right)}}}{{{C_{1}\left( \frac{p^{*}}{p_{s}} \right)}\left( {1 - \Phi^{2}} \right)} + {C_{2}\left( {1 - \Phi} \right)} + \frac{\text{?}}{{E_{s}\left( {1 - \frac{p^{*}}{p_{2}}} \right)}\left( \frac{p^{*}}{p_{s}} \right)}}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (8)\end{matrix}$

Using Equation 8 with Es=90.15 MPa,

s=1,073 MPa, Φ=1, po=101.325 kPa, ν*=0.33, and C1=0.311 for EML227 andC1=0.181 for EML350, the elastic moduli of EML227 and EML350 wereaccurately predicted with an error within ±1%. Furthermore, the areasunder the stress-strain curve in the elastic region, bounded below 6.8%strain for EML227 and 7.8% strain for EML350, corresponding to theelastic limits, were found to be predicted with good agreement with theexperimental results when the elastic moduli are based on Equation 8. Onthe contrary, the scaling laws of either open-cell or closed-cell resultin an error of over 50%, which further validate the inventive model andconfirm the semi-closed cell structure of the foam. In the plateauregion, all tested foams show an increase in the stress corresponding toa large increase in the strain, which as discussed earlier is a distinctcharacteristic of closed-cell foams. That is to say, the closed-cellbehavior is dominating the response of specifically polyurea foams fromthe outset of the elastic region to the onset of the densificationregion. Nonetheless, and regardless of the base material, all testedfoams have nearly the same onset of densification at ˜42% strain, bycarefully identifying the inflection point on the stress-strain curverather than neglecting the plateau region for foams with relativedensities higher than 0.3 (see Equation 5).

Considering the plateau region, which is important for impact mitigationapplications, allowed us to compute the effectiveness of the testedfoams in dissipating the incoming impact energy through the area underthe stress-strain curve corresponding to this region. Thus, EMT 350encloses the largest area under the stress-strain curve in the plateauregion with ˜71.7 kJ/m3, which compares to merely half the energy of32.3 kJ/m3 for EML 227 foam. Furthermore, the energy encompassed by thestress-strain data in the plateau region for the benchmark foam liesbetween the new polyurea foams at 51.9 kJ/m3, demonstrating thesuperiority of our novel foam based on energy dissipated per unit mass.

Example Efficiency and G-Level

FIG. 25 shows the predicted performance of polyurea foams in comparisonto a benchmark closed-cell foam based on efficiency and G-level indynamic loading scenarios calculated from the quasi-statically measuredstress-strain curve as discussed earlier. In essence, the quasi-staticdata is used to make predictions about the performance of these foams inhigh impact loading scenarios.

FIG. 25 reports four important predictions to explicate the superiorityof our novel foams.

First, regardless of the evaluation metric, EML227 outperforms the othertwo types of tested foams, where the maximum efficiency and minimumG-level were found to be 23%, and 254, respectively. These levels are22% and 36% higher than those reported for the denser polyurea foamcounterpart, respectively.

Second, the peak of the maximum efficiency associated with EML227 occursat a lower dynamic stress than those for EMT 350 and benchmark foams,which indicates that while EML227 is suitable for low impactapplications, the others should be considered for applications whenhigher dynamic stresses are forecasted. Basically, using the samemanufacturing process and the same base materials, FIG. 25 shows theability to tailor the foam properties for a specific applicationdepending on the range of expected dynamic stresses.

Third, the predictions of the maximum efficiency and minimum G-Level areranked based on the amplitudes such that the performance of thebenchmark foam is always shown to lie between the performance of thepolyurea foams. Interestingly, the same ranking was observed as shown inFIG. 24 and discussed earlier in relation to the onset of densificationat a strain of ˜42%. In other words, the effectiveness of a foammaterial in an impact mitigation scenario is hinged on its mechanicalresponse prior to the onset of densification.

Finally, the ability of EML227 to decelerate an incoming impact mass wasshown to be superior in comparison to the other two tested foams, whichis shown by having a minimum G-Level that is 36% and 31% lower than bothEMT 350 and the benchmark foams, respectively.

The effectiveness of EML227 foam to reduce the severity of the impact isthought to be associated with the underlying semi-closed cellmicrostructure. The latter point is further elucidated by comparing theG-Level of EML350 to a 12% heavier completely closed-cell benchmarkfoam, which shows a comparable effectiveness in mitigating impacts whilemaintaining a lower weight penalty.

Example Other Isocyanate Compounds

A wide variety of polyisocyanate compounds (a) may be used for theinvention. The polyisocyanate will preferably have a functionality inthe range 2 to 3, more preferably 2 to 2.7. The polyisocyanate ispreferably aliphatic or aromatic. The most preferred polyisocyanate isdiphenyl methane diisocyanate (MDI) and its derivatives conventionallyused to obtain a liquid product (e.g. polyphenylene polymethylenepolyisocyanate). The preferred derivative would be auretonimine/carbodiimide modification of pure MDI, for example Isonate143 L (ex DOW) or their mixtures with quasi prepolymers, e.g. IsonateRMA 400 (ex DOW). The diisocyanates may also be fluorinated, brominated,or chlorinated derivatives.

Further aromatic polyisocyanates which may be used in the process of theinvention are those exemplified in columns 3 and 4 of U.S. Pat. No.4,487,908 and column 3 of U.S. Pat. No. 4,126,742. Aryl groups andheteroaryl group-containing compounds may also be used.

Further examples of polyisocyanates which may be used are alicyclic andheterocyclic diisocyanates, e.g. furan diisocyanates.

The amount of the polyisocyanate used in the reaction is preferably suchthat the equivalent ratio of isocyanate to amino is in the range 4:1 to20:1, more preferably 7:1-15:1, e.g. ca 10:1. Use of stoichiometricratios less than 4 causes high mould filling viscosity and a very shortgel time (thus rendering the materials unsuitable for processing).

EXAMPLE Amine Compounds

The polyamino compounds (b) used in the invention include a flexiblechain, i.e. one with a glass transition temperature (T.sub.g) well belowambient temperature.

The preferred polyaminos (b) are high molecular weightamino-functionalized (preferably amino-terminated) polyether basedmaterials. The polyether backbone is preferably polyalkylene oxidebackbone, preferably one in which the alkylene residue has 2-4 carbonatoms. The polyether based materials used in the invention preferablyhave a molecular weight of 200-12000 and a functionality in the range2-8. The preferred functionality is 2 or 3. If a polyether polyaminowith a functionality of 2 is used, then preferably the polyetherpolyamino has a molecular weight in the range 500-10000, most preferably2000-4000. If the polyamino has a functionality of 3, then its molecularweight is preferably in the range 400-10000, more preferably 3000-6000.

Suitable polyether polyaminos for use in the invention are the VERSALINKproducts which are specialty polymeric, non-toxic diamines of varyingmolecular weights. Additionally, Jeffamine products may be used and areavailable from Texaco.

Other polyaminos which may be used are based on silicones, butadienes,isobutylenes, and isoprenes as well as copolymers thereof with othermonomers, e.g. a copolymer of butadiene and acrylonitrile.

The chain extender (c) is optional but if used enables control of moldfilling viscosity, gel time and modulus material to be produced. Thechain extender (c) is preferably an amino having at least two aminogroups each bonded to a ring and preferably sterically shielded, e.g. byalkyl groups. The ring structure(s) may be aromatic, quasi-aromatic,allcyclic, or heterocyclic. The attachment of the amino groups to a ringreduces the reactivity of the amino group so that the reaction with thepolyisocyanate is slower than for (b). Preferably there is a maximum oftwo ring systems in the chain extender molecule.

The chain extender may for example be of the general formula (I): arylhaving one or more R groups and two —NH2 amines, where the R groups arethe same or different alkyl groups preferably having 3-10 substituted orunsubstituted carbon atoms. The preferred chain extender of formula (I)is diethyl toluene diamine (DEDTA) which is a mixture of compounds.

Further examples of chain extenders which may be used have two aromaticring systems connected directly or indirectly to each other, e.g. via amethylene group.

The presence of a methylene group between the two aromatic nuclei inFormula (III) provides a limited amount of flexibility in the chainextender.

The analogous cycloaliphatic derivatives (i.e. in which the aromaticnuclei are hydrogenated) may also be used.

The preferred compounds are MDIPA (methylene bis-2,6-diisopropylaniline) and M.MIPA (methylene bis 2-methyl-6-isopropyl aniline)together with their mixtures with DEDTA.

It is of course possible to use mixtures of the compounds.

Other amino functional chemicals such as aliphatic diamines, napthalenicdiamines liquid mixtures of the polyphenylene polymethylene polyaminosof the type obtained from aniline formaldehyde condensation may also beused.

The chain extender (c) when used is present in the reactant mixture inan amount not greater than five equivalents of (c), more preferably notmore than 3 equivalents, more preferably not more than 1 equivalents perequivalent of polyamino (b). Use of higher amounts of (c) causes highmould filling viscosity and a very short gel time and thus the materialsare unsuitable for processing.

As primary aliphatic polyamines having as a curing agent in epoxy groupsor isocyanate groups, amine PA are suitable for the formula (II) in afirst embodiment are known curable compositions, in particular thefollowing:

Aliphatic, cycloaliphatic or arylaliphatic primary diamines, such as inparticular ethylene diamine, 1,2-propanediamine, 1,3-propanediamine,2-methyl-1,2-propanediamine, 2,2-dimethyl-1,3-propanediamine,1,3-butanediamine, 1,4-butanediamine, 1,3-pentanediamine (DAMP),1,5-pentanediamine, 1,5-diamino-2-methylpentane (MPMD),2-butyl-2-ethyl-1,5-pentanediamine (C11-Neodiamin), 1,6-hexanediamine,2,5-dimethyl-1,6-hexanediamine, 2,2,4- and2,4,4-trimethylhexamethylenediamine (TMD), 1,7-heptanediamine,1,8-Octandiamin, 1,9-nonanediamine, 1,10-decanediamine,1,11-undecanediamine, 1,12-dodecane diamine, 1,2-, 1,3- and1,4-diaminocyclohexane, bis (4-aminocyclohexyl) methane (H12-MDA), bis(4-amino-3-methylcyclohexyl) methane, bis (4-amino-3-ethylcyclohexyl)methane, bis (4-amino-3,5-dimethylcyclohexyl) methane, bis(4-amino-3-ethyl-5-methyl-cyclohexyl)-methane (M-MECA),1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (=isophoronediamine orIPDA), 2- and 4-methyl-1,3-diaminocyclohexane and mixtures thereof, 1,3-and 1,4-bis (aminomethyl) cyclohexane, 2,5 (2,6) -bis-(aminomethyl)bicyclo [2.2.1] heptane (NBDA), 3 (4), 8 (9) -bis-(aminomethyl) tricyclo[5.2. 1.0 2, 6] decane, 1,4-diamino-2,2,6-trimethylcyclohexane (TMCDA),1,8-menthane diamine, 3,9-bis (3-aminopropyl)-2,4,8,10 tetraoxaspiro[5.5] undecane as well as 1,3- and 1,4-xylylenediamine.

Also suitable are aliphatic, cycloaliphatic or arylaliphatic primarytriamines such as 4-aminomethyl-1,8-octanediamine, 1,3,5-tris(aminomethyl) benzene, 1,3,5-tris (aminomethyl) cyclohexane, tris (2aminoethyl) amine, tris (2-aminopropyl) amine, tris(3-aminopropyl)-amine.

Also suitable are ether-containing aliphatic primary diamines, such asin particular bis (2-aminoethyl) ether, 3,6-dioxaoctane-1,8-diamine,4,7-dioxadecane-1,10-diamine, 4,7-dioxadecane-2, 9-diamine,4,9-dioxadodecane-1,12-diamine, 5,8-dioxadodecane-3,10-diamine,4,7,10-trioxatridecane-1,13-diamine and higher oligomers of thesediamines, bis (3-aminopropyl) polytetrahydrofurans and otherpolytetrahydrofuran-diamine, and polyoxyalkylene diamines. The latterare typically products from the amination of polyoxyalkylene diols, andare available, for example under the name Jeffamine® (from Huntsman),under the name polyetheramine (from BASF) or under the name PC Amine®(from Nitroil). Particularly suitable polyoxyalkylene diamines areJeffamine® D-230, Jeffamine® D-400, Jeffamine® D-2000, Jeffamine®D-4000, Jeffamine® XTJ-511, Jeffamine® ED-600, Jeffamine® ED-900,Jeffamine® ED-2003, Jeffamine®XTJ-568, Jeffamine® XTJ-569, Jeffamine®XTJ-523, Jeffamine® XTJ-536, Jeffamine® XTJ-542, Jeffamine®XTJ-559,Jeffamine® EDR-104, Jeffamine® EDR 148, Jeffamine® EDR-176;Polyetheramine D 230, polyetheramine D 400 and Polyetheramine D 2000, PCamines® DA 250, PC amines® DA 400, DA 650 and PC amines® PC amines® DA2000;

Also suitable are primary polyoxyalkylene triamines, which are typicallyproducts from the amination of polyoxyalkylene triols and, for example,are available under the name Jeffamine®(from Huntsman), under the nameof the polyetheramines (from BASF) or under the name PC amines® (ofNitroil) such as especially Jeffamine® T-403, Jeffamine® T-3000,Jeffamine® T-5000, T 403 polyetheramine, polyetheramine T 5000, and PCamines® TA 403.

Also suitable are polyamines containing tertiary amino groups with twoprimary aliphatic amino groups, such as in particularN,N′-bis(aminopropyl)piperazine, N,N-bis(3-aminopropyl) methylamine,N,N-bis(3-aminopropyl)ethylamine, N,N-bis(3-aminopropyl) propylamine,N,N-bis(3-aminopropyl)cyclohexylamine,N,N-bis(3-aminopropyl)-2-ethyl-hexylamine, as well as the products fromthe double cyanoethylation and subsequent reduction of fatty amines,which are derived from natural fatty acids, such asN,N-bis(3-aminopropyl) dodecylamine, andN,N-bis(3-aminopropyl)-talgalkylamin, available as TriameenφY12D andTriameen YT® (ex Akzo Nobel).

Also suitable are Polyamines containing tertiary amino groups with threeprimary aliphatic amino groups, such as in particular tris(2-aminoethyl) amine, tris (2-aminopropyl) amine and tris(3-aminopropyl) -amine.

Various of the above-disclosed and other features and functions, oralternatives thereof, may be combined into many other different systemsor applications. Various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art, each of which is alsointended to be encompassed by the disclosed embodiments.

Having described embodiments for the invention herein, it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments of the inventiondisclosed which are within the scope and spirit of the invention asdefined by the appended claims. Having thus described the invention withthe details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

What is claimed:
 1. A process of making a hybrid polyurea foam having asemi-closed cell microstructure, comprising the steps in a reactionhaving a ratio of 4:1 by mass of an amine compound to an isocyanatecompound, and having a ratio of 8:3 by mass of the amine compound andthe isocyanate compound to deionized water: STEP
 1. Mixing deionizedwater and an amine compound in a mixing container at high speed; STEP 2.With the mixer turned off, adding the isocyanate compound to the mixingcontainer, then mixing at high speed the solution ofisocyanate-water-amine to a foam; and, STEP 3: Letting the solution sitafter mixing, allowing time for the isocyanate-water-amine-reaction tooccur, and then, after draining excess water from the mixing container,pour the mixture into a mold.
 2. The process of claim wherein theisocyanate has the formulaOCN—R₁—NCO, where R₁ is substituted or unsubstituted alkyl or arylhaving 3-10 carbons; and the polyamine has the formulaH₂N—R₂—NH₂ where R₂ is substituted or unsubstituted alkyl or aryl having3-10 carbons.
 3. The hybrid polyurea foam of claim 1, wherein the hybridpolyurea foam is configured in a complex geometry or shape selected fromthe group consisting of: padding foam for helmets, outsoles for walkingshoes, outsoles for running shoes, and padding foam for body armor. 4.The process of claim 1, wherein the isocyanate is selected from thegroup consisting of an aromatic diisocyanate, toluene diisocyanate(TDI), methylenediphenyl diisocyanate (MDI), p-phenylene diisocyanate(PPDI), naphthalene diisocyanate (NDI), an aliphatic diisocyanate,hexamethylene diisocyanate (HDI), methylene dicyclohexyl diisocyanate orhydrogenated MDI (HMDI), isophorone diisocyanate (IPDI), and mixturesthereof.
 5. The process of claim wherein the amine is a Versalink amine.6. A hybrid polyurea foam made according to the process of claim 1,wherein the hybrid polyurea foam comprises: (i) a plurality of largesemi-closed cells having an average diameter of 200-500 μm, surroundedby (ii) a plurality of small semi-closed cells having an averagediameter of 30-90 μm.
 7. A process of making a hybrid polyurea foamhaving a semi-closed cell microstructure, comprising the steps in areaction having a ratio of 4:1 by mass of an amine compound to anisocyanate compound, and having a ratio of 8:3 by mass of the aminecompound and the isocyanate compound to deionized water: STEP 1:Removing crystallization in a sample of methylene diphenyl diisocyanate(Isonate) by heating the Isonate to about 98 degrees Fahrenheit, holdingat that temperature for about 45 minutes, then immediately stirringvigorously for 2 minutes, and allowing Isonate to return to roomtemperature; STEP 2: Pre-Mixing a sample of deionized water and a sampleof polytetramethyleneoxide-di-p-aminobenzoate (Versalink) in a mixingcontainer for about 45 seconds at about 10,000 rpm, wherein the ratio ofVersalink to Isonate is 4:1 by mass, and the ratio of the combination ofVersalink and Isonate to Deionized water is 8:3 by mass; STEP 3: Withthe mixer turned off and suspended above the mixing container, add theIsonate to the mixing container, then mix the solution of deionizedwater-Versalink-Isonate for 45 seconds at roughly 10,000 RPM, moving themixer around the mixing container during mixing; and, STEP 4: Let thesolution sit for 45 seconds after mixing, allowing time for the reactionto occur, and then, after draining excess water from the mixingcontainer, pour the mixture into a mold.
 8. A hybrid polyurea foam madeaccording to the process of claim 7, wherein the hybrid polyurea foamcomprises: (i) a plurality of large semi-closed cells having an averagediameter of 370+/−162 μm, surrounded by (ii) a plurality of smallsemi-closed cells having an average diameter of 69+/−162 μm.
 9. Thehybrid polyurea foam of claim 8, wherein the hybrid polyurea foam isconfigured in a complex geometry or shape selected from the groupconsisting of: padding foam for helmets, outsoles for walking shoes,outsoles for running shoes, and padding foam for body armor.
 10. Amethod of preparing a polyurea component in a pre-treated non-stickmold, comprising the steps in order: STEP 1: Measure out the necessaryamounts of the following ingredients: (a) Versalink P-1000(polytetramethyleneoxide-di-p-aminobenzoate); (b) Isonate 143L(methylene diphenyl diisocyanate)-(b)(i) The ratio of Versalink toIsonate must be 4:1 by mass; (c) Deionized Water-(c)(i) The ratio of thecombination of Versalink and Isonate to Deionized water must be 8:3 bymass; (d) To produce a foam sample with a thickness of 0.75 in, use thefollowing masses: Versalink: 429.9 g, Isonate: 107.5 g, Deionized Water:1,433.0 g; STEP 2: Heat Isonate to 98 degrees Fahrenheit. Hold at thistemperature for 45 minutes, then immediately stir vigorously for 2minutes. Allow Isonate to return to room temperature. (a) This is doneto break up any crystallization in the Isonate; STEP 3: Pre-Mixing(Deionized water and Versalink): (a) Add the deionized water and thenthe Versalink to a mixing container, (b) Use the SCILOGEX D500Homogenizer to mix the solution for 45 seconds at a Low setting, roughly10,000 RPM, moving the mixer around the mixing container during mixing;STEP 4: Mixing (Deionized water, Versalink, and Isonate): (a) With themixer turned off and suspended above the mixing container, add theisonate to the mixing container, (b) Use the SCILOGEX D500 Homogenizerto mix the solution for 45 seconds on a low setting, roughly 10,000 RPM,moving the mixer around the mixing container during mixing; STEP 5:Waiting period: (a) Let the solution sit for 45 seconds after mixing.This allows time for the reaction to occur; STEP 6: Immediately afterthe waiting period, drain excess water from the bottom of the mixingcontainer; STEP 7: Pour mixture into the mold, as evenly as possible;STEP 8: drain excess water by tilting the mold in multiple directions;STEP 9: place the mold lid into the mold, and attach bar clamps (1 perside, 4 total) to limit the expansion of the foam and inhibit the lidfrom rising or becoming uneven; and STEP 10: Leave sample in mold for 24hours, after 24 hours, remove the mold from the polyurea foam component.11. A polyurea component prepared according to the process of claim 10,wherein the polyurea component is configured in a complex geometry orshape selected from the group consisting of : padding foam for helmets,outsoles for walking shoes, outsoles for running shoes, and padding foamfor body armor.
 12. A polyurea foam having semi-closed cells, whereinthe cell face has 3-10% holes, where it is 20% more efficient thanstandard prior polyurea foams, 44% better strength than standard priorpolyurea foams, 15% better toughness than standard prior polyurea foams,29% better specific modulus of elasticity than standard prior polyureafoams, where the foam is mostly made of large cells 200-500 μm acrosssurrounded by small cells 30-90 μm across, wherein the foam is uniformin its mix of large cells surrounded by small cells and does not have adense edge portion having stiff closed cell struts and small cellsheaths with a less dense inner portion, where the foam is functions inthe elastic portion like closed cells and functions in the plateauregion like open cell foams.